1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device for providing data in a time-divided manner to left and right pixel regions of one data line, thereby reducing the number of source drive ICs, expensive component.
2. Discussion of the Related Art
Recently, with the increasing development of an information-based society, demands for various display devices have increased. Accordingly, much effort has been expended to research and develop various flat display devices such as a liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD), and some species of the flat display devices are already applied to displays of various equipment.
Among the various flat display devices, the liquid crystal display (LCD) device has been most widely used due to advantageous characteristics of thinness, lightness in weight, and low power consumption, whereby the LCD device substitutes for Cathode Ray Tube (CRT). In addition to the mobile type LCD devices such as a display for a notebook computer, the LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in the LCD technology with applications in different fields, research in enhancing the picture quality of the LCD device has been in some respects lacking as compared to other features and advantages of the LCD device. In order to use the LCD device in various fields as a general display, the key to developing the LCD device lies on whether the LCD device can implement a high quality picture, such as high resolution and high luminance with a large-sized screen while still maintaining lightness in weight, thinness, and low power consumption.
Generally, the LCD device is driven according to the optical anisotropy and polarizability of the liquid crystal. Liquid crystal molecules are aligned with directional characteristics since the liquid crystal molecules respectively have long and thin shapes. In this respect, an electric field is applied to the liquid crystal for controlling the alignment direction of the liquid crystal molecules. That is, if the alignment direction of the liquid crystal molecules is controlled by the electric field, the light is polarized and changed by the optical anisotropy of the liquid crystal, thereby displaying the picture image.
The liquid crystal is classified into a positive (+) type liquid crystal having positive dielectric anisotropy and a negative (−) type liquid crystal having negative dielectric anisotropy according to electrical characteristics of the liquid crystal. In the positive (+) type liquid crystal, a longitudinal axis of a positive (+) liquid crystal molecule is parallel to the electric field applied to the liquid crystal. Meanwhile, in the negative (−) type liquid crystal, a longitudinal axis of a negative (−) liquid crystal molecule is perpendicular to the electric field applied to the liquid crystal.
Recently, an active matrix LCD (AM-LCD), in which a thin film transistor and a pixel electrode connected to the thin film transistor are arranged in a matrix, has attracted considerable attention due to the ability to display high resolution and great moving picture images. The AM-LCD device largely includes an LCD panel displaying a picture image and a driving part applying a driving signal to the LCD panel. Also, the LCD panel includes first and second glass substrates bonded to each other at a predetermined interval and a liquid crystal layer injected between the first and second glass substrates.
The first glass substrate (TFT array substrate) includes a plurality of gate and data lines, a plurality of pixel electrodes, and a plurality of thin film transistors. The plurality of gate lines are formed on the first glass substrate at fixed intervals in one direction and the plurality of data lines are formed at fixed intervals perpendicular to the plurality of gate lines. The plurality of pixel electrodes in the matrix are respectively formed in pixel regions defined by the plurality of gate and data lines crossing each other. The plurality of thin film transistors are switched according to signals of the gate lines for transmitting signals of the data lines to the respective pixel electrodes.
Also, the second glass substrate (color filter substrate) includes a black matrix layer excluding light from regions except the pixel regions of the first substrate, R/G/B color filter layer displaying various colors, and a common electrode obtaining the picture image. Next, a predetermined space is maintained between the first and second glass substrates by spacers, and the first and second substrates are bonded to each other by a sealant pattern having a liquid crystal injection inlet. The liquid crystal layer is injected between the first and second glass substrates.
The thin film transistor TFT-LCD device is classified into an amorphous silicon type and a polysilicon type according to characteristics of a semiconductor layer. For improving yield in the amorphous silicon and polysilicon types, it is important to simplify manufacturing process steps. That is, the amorphous silicon uses a Chemical Vapor Deposition CVD method at a low temperature, so that it is useful for the LCD device using the glass substrate. However, the amorphous silicon type has low carrier mobility and thus is not appropriate for a transistor of a drive IC requiring a rapid operation time. Thus, an additional drive IC driving the LCD device is required and attached to the periphery of the LCD panel. The additional drive IC complicates the manufacturing process steps, thereby increasing manufacturing cost.
In comparison with the amorphous silicon type, the polysilicon type has a large carrier mobility, so that it is appropriate for forming the drive IC. In this case, when using the polysilicon as the semiconductor layer for the thin film transistor of the LCD device, it is possible to form the thin film transistor for the pixel electrode, and the transistor for the drive IC on the same glass substrate, thereby decreasing manufacturing cost by obtaining simplified manufacturing process steps for the module and realizing low power consumption.
Hereinafter, a pixel structure of a related art LCD device will be described with reference to the accompanying drawings. FIG. 1 is a plan view illustrating the pixel of the related art LCD device, and FIG. 2 is a cross-sectional view taken along line A-A′ of FIG. 1.
As shown in FIG. 1, the related art LCD device includes a plurality of gate lines 11, and a plurality of data lines 12 perpendicular to the respective gate lines 11 at fixed intervals. At this time, a plurality of pixel regions are defined by the plurality of gate and data lines 11 and 12 crossing each other. Also, a thin film transistor TFT is formed at each crossing point of the gate and data lines 11 and 12, and a pixel electrode 13 is formed in each pixel region that is connected to a drain electrode 12b of the thin film transistor TFT.
A structure of the thin film transistor will be described with reference to FIG. 2. Referring to FIG. 2, a gate electrode 11a protruding from the gate line 11 is formed on a glass substrate 10, and then a gate insulating layer 15 is formed on an entire surface of the glass substrate 10 including the gate electrode 11a. After that, a semiconductor layer 16 is formed on the gate insulating layer 15 above the gate electrode 11a, and then source and drain electrodes 12a and 12b are formed on both sides of the semiconductor layer 16. Then, a passivation layer 17 is formed on the entire surface of the semiconductor layer 16 and the drain electrode 12b, and the pixel electrode 13 is connected with the drain electrode 12b. 
FIG. 3 is an equivalent circuit diagram of the pixel structure in the LCD device of FIG. 1. As shown in FIG. 3, the plurality of thin film transistors TFTs are formed at the respective crossing points between the plurality of gate lines G1, G2, . . . , Gn−1, Gn and data lines S1, S2, . . . , Sn−1, Sn, and a liquid crystal capacitor CLC is connected to the drain electrode of the thin film transistor. The liquid crystal capacitor CLC is not an additional device, but is formed of liquid crystal serving as dielectric defining the pixel electrode of the first substrate, and the common electrode of the second substrate as first and second electrodes. The liquid crystal capacitor CLC maintains a data voltage value charged in each pixel electrode at a predetermined time period.
Although not shown, an additional storage capacitor Cst is formed between the pixel electrode and the common electrode, so that it is possible to control charging time of liquid crystal. Meanwhile, when forming the polysilicon thin film transistor TFT, a selector switch is mounted in the substrate. At this time, two data lines are driven with one output applied from a source drive IC to each data line, so that it is possible to reduce the number of source drive ICs, and to increase contact pitch. However, the related art has limitation in that the number of data lines is not reduced in the pixel structure. Also, it is required to obtain the selector switches corresponding to output lines in an output terminal of the source drive IC. Furthermore, the entire size becomes large due to the selector switches.
A driving method of the LCD device will be described with reference to FIG. 3. When a driving voltage (pulse signal) is applied to each gate line G1, G2, . . . , Gn−1, Gn, each thin film transistor TFT connected to the corresponding gate line G1, G2, . . . , Gn−1, Gn is turned on. Thus, the data voltage applied to each data line S1, S2, . . . , Sn−1, Sn is applied to the pixel electrode, so that the data voltage is charged. At this time, the data voltage is charged in each pixel electrode 13 at a cycle of one frame, and then is maintained when the next signal is applied thereto.
Each pixel electrode of the LCD device is independently driven according to a scanning signal applied to each gate line G1, G2, . . . , Gn−1, Gn. Herein, the driving method of the LCD device will be described on the basis of voltage discharge of the corresponding pixel according to the operation of one thin film transistor.
In a selection block Ts of a predetermined gate line, a voltage Vg(on) is applied to the gate line connected to a gate drive IC, which is higher than that of the data line, so that a channel resistance becomes low between drain and source electrodes. Also, the voltage output from a source drive IC to each data line is applied to liquid crystal layer through the pixel electrode. In a non-selection block Tns of the predetermined gate line, a voltage Vg(off) is applied to the gate line, which is lower than that of the data line, whereby the drain electrode is electrically insulated from the source electrode, thereby maintaining electric charge in the liquid crystal layer during the selection block Ts. Thus, when applying the voltage Vg(on) to the gate line, the voltage is applied to the liquid crystal layer by charging each pixel electrode through the data line.
As a controlling RMS voltage is applied to the liquid crystal layer between the pixel electrode and the common electrode, linearly polarized light passing through a polarizing plate is changed by passing through the liquid crystal layer, and then is selectively transmitted by an analyzing plate, thereby displaying information as luminosity of the pixel. Also, polarity of the voltage applied to the liquid crystal layer is controlled at each cycle by controlling wave of the voltage applied to the data line and the common electrode (not shown), thereby preventing electrochemical reaction of liquid crystal molecules.
At this time, one cycle Tf of the scanning signal is a total of the selection block Ts and the non-selection block Tns. When transmitting a picture at 60 Hz, one cycle is about 16.7 msec, and the selection block Ts is about 21.7 μsec (=16.7 msec/768) in case of an XGA class display (1024×768 pixels). For maintaining the voltage applied to the pixel electrode 13 in the selection block Ts during the non-selection block Tns, the storage capacitor Cst (not shown) is provided in parallel with the liquid crystal capacitor CLC. At this time, the storage capacitor Cst is formed of one electrode of the preceding gate line or one electrode of an additional storage line. Also, the storage capacitor Cst is comprised of the pixel electrode opposing to the one electrode, and the gate insulating layer or the passivation layer between the two electrodes.
However, the related art LCD device has the following disadvantages.
If the related art is applied to a high resolution panel, the number of gate and data lines forming the pixel regions is increased, so that it is necessary to obtain the plurality of gate drive ICs and source drive ICs corresponding to the number of the gate and data lines, respectively.
For example, for an XGA class display (1024×768), the related art LCD device requires eight source drive ICs, each having 384 pins, and three gate drive ICs, each having 256 pins, corresponding to the 3072 data lines (since one pixel is comprised of R, G and B sub pixels, 1024×3) and 768 gate lines.
At this time, the source drive IC is more expensive than the gate drive IC. In addition, the source drive IC has a power consumption of about 100 mW while the gate drive IC has power consumption of about 20 mW. Since the number of the source drive ICs is greater than the number of the gate drive ICs, the manufacturing cost and power consumption are determined according to the number of the source drive ICs.
Also, when obtaining high resolution in the same size panel, the width of each of the pixels becomes smaller, so that it becomes harder to form a Chip On Film COF or Tape Carrier Package TCP for mounting the drive IC corresponding to the pixel structure.